U.S. patent number 8,130,177 [Application Number 12/677,889] was granted by the patent office on 2012-03-06 for organic el display panel and manufacturing method thereof.
This patent grant is currently assigned to Panasonic Corporation. Invention is credited to Shuhei Nakatani, Kiyohiko Takagi.
United States Patent |
8,130,177 |
Nakatani , et al. |
March 6, 2012 |
**Please see images for:
( Certificate of Correction ) ** |
Organic EL display panel and manufacturing method thereof
Abstract
Provided is a technique which easily forms a bank the inner
lateral surface of which has a part (lower part of the inner
lateral surface) made to be lyophilic. The technique provides an
organic EL display panel containing a plurality of organic EL
elements in which each organic EL element comprises a substrate, an
anode disposed on the substrate, an organic light emitting layer
disposed on the anode, a cathode disposed on the organic light
emitting layer, and a forward-tapered bank which regulates the area
of the organic light emitting layer. A lyophobic organic film is
disposed on the upper surface of the bank and the surface of the
upper part of the tapered portion of the bank but not disposed on
the surface of the lower part of the tapered portion of the bank of
the organic EL element.
Inventors: |
Nakatani; Shuhei (Osaka,
JP), Takagi; Kiyohiko (Osaka, JP) |
Assignee: |
Panasonic Corporation (Osaka,
JP)
|
Family
ID: |
41064912 |
Appl.
No.: |
12/677,889 |
Filed: |
February 10, 2009 |
PCT
Filed: |
February 10, 2009 |
PCT No.: |
PCT/JP2009/000538 |
371(c)(1),(2),(4) Date: |
March 12, 2010 |
PCT
Pub. No.: |
WO2009/113239 |
PCT
Pub. Date: |
September 17, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100289728 A1 |
Nov 18, 2010 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 13, 2008 [JP] |
|
|
2008-064818 |
|
Current U.S.
Class: |
345/76; 313/506;
313/498 |
Current CPC
Class: |
H01L
27/3246 (20130101); H01L 51/0003 (20130101) |
Current International
Class: |
G09G
3/30 (20060101) |
Field of
Search: |
;345/76-81 ;313/498-512
;425/24 ;445/24 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2002-237383 |
|
Aug 2002 |
|
JP |
|
2004-171007 |
|
Jun 2004 |
|
JP |
|
2005-326799 |
|
Nov 2005 |
|
JP |
|
2006-073222 |
|
Mar 2006 |
|
JP |
|
2006-188487 |
|
Jul 2006 |
|
JP |
|
2006-216297 |
|
Aug 2006 |
|
JP |
|
2007/0005056 |
|
Jan 2007 |
|
JP |
|
2007-005056 |
|
Jan 2007 |
|
JP |
|
2007-095512 |
|
Apr 2007 |
|
JP |
|
2007-324033 |
|
Dec 2007 |
|
JP |
|
Other References
International Search Report that issued with respect to
PCT/JP2009/000538, mailed Mar. 10, 2009. cited by other .
Search report from E.P.O. that issued with respect to patent family
member European Patent Application No. 09719875.8 on Feb. 15, 2011.
cited by other.
|
Primary Examiner: Mengistu; Amare
Assistant Examiner: Bolotin; Dmitriy
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
1. An organic EL display panel comprising a plurality of organic EL
devices each including: a substrate; an anode formed over the
substrate; an organic emitting layer formed over the anode, the
organic emitting layer having a uniformly-thick area; a cathode
formed over the organic emitting layer; a forward tapered bank
defining a region for the organic emitting layer, the bank having a
top surface and an inclined side surface, the bank being in contact
with the anode and made entirely of organic insulating material;
and a lyophobic organic film formed on the top surface of the bank
and a upper portion of the inclined side surface of the bank,
wherein a lower portion of the inclined side surface of the bank
includes no lyophobic organic film, and the organic emitting layer
is formed by a coating method, a contact point between a surface of
the organic emitting layer, which surface faces the cathode, and
the inclined side surface of the bank is at a boundary between a
region with the lyophobic organic film and a region without the
lyophobic organic film, and the contact point structured and
arranged above the uniformly-thick area of the organic emitting
layer.
2. The organic EL display panel according to claim 1, wherein the
forward tapered bank has a taper angle of 20.degree. to
70.degree..
3. The organic EL display panel according to claim 1, wherein the
lyophobic organic film formed on the bank surface is a
self-assembled film.
4. The organic EL display panel according to claim 1, wherein the
lyophobic organic film formed on the bank surface is a monolayer
film.
5. The organic EL display panel according to claim 1, further
comprising a lyophilic organic film formed on the lower portion of
the inclined side surface of the bank.
6. A method of manufacturing an organic EL display panel
comprising: providing a substrate having a plurality of anodes
formed thereon; forming a forward tapered bank having a top surface
and an inclined side surface so as to surround at least a part of
the anode, the bank being in contact with the anode and made
entirely of organic insulating material; forming a lyophobic
organic film over a surface of the bank; exposing the lyophobic
organic film at a lower portion of the inclined side surface of the
bank so as to reduce the lyophobicity of the exposed portion of the
lyophobic organic film or remove the exposed portion of the
lyophobic organic film; applying an ink containing organic
luminescent material in a region defined by the bank to form
therein an organic emitting layer having a uniformly-thick area;
and forming a cathode over the organic emitting layer, wherein a
contact point between a surface of the organic emitting layer,
which surface faces the cathode, and the inclined side surface of
the bank is at a boundary between a region with the lyophobic
organic film and a region without the lyophobic organic film, and
the contact point structured and arranged above the uniformly-thick
area of the organic emitting layer.
7. The method according to claim 6, wherein the forward tapered
bank has a taper angle of 20.degree. to 70.degree..
8. The method according to claim 6, wherein the lyophobic organic
film is a lyophobic, photosensitive self-assembled film.
9. The method according to claim 6, wherein light used for the
exposure is UV light.
10. The method according to claim 6, further comprising forming a
hole injection layer over the anode prior to the bank formation
step.
Description
TECHNICAL FIELD
The present invention relates to an organic EL display panel and a
manufacturing method of the same.
BACKGROUND ART
An organic EL display panel includes a plurality of organic EL
devices formed on a substrate, each of which typically includes a
pair of electrodes consisting of pixel electrode (anode) and a
cathode, and functional layers such as an organic emitting layer
between the electrodes. The electrodes and functional layers are
generally formed by vapor deposition, sputtering or other method,
but can also be formed by coating method.
Formation of the electrodes and functional layers by coating method
involves application and drying of liquid substances in regions
defined by bank made of insulating material. Failure to
appropriately control the bank's surface affinity for the liquid
substances often leads to low uniformity in the resultant layer's
thickness. This in turn leads to poor image characteristics in the
manufactured organic EL display panel due in part to brightness
unevenness.
In general, the bank top surface needs to be lyophobic in order for
the applied liquid substance to be retained in the region defined
by the bank. However, when the bank inner side surface is
lyophobic, the applied liquid substance fails to spread to the
desired region, which results in low uniformity in the resultant
layer's thickness. Accordingly, a lower side of the bank inner side
surface of the bank is preferably lyophilic, while a upper side of
the inner side surface of the bank is lyophobic.
To achieve this, two-layered banks have been reported in which the
lower layer is made lyophilic and the upper one is made lyophobic
(see Patent Documents 1 to 5). For example, these literatures
describe supplying liquid substances in regions defined by
two-layered bank consisting of a lower layer made of inorganic
material and a upper layer made of organic material or the like, to
form therein functional layers such as an organic emitting layer.
Moreover, techniques have also been known that form a lyophobic
organic film only on the upper layer of the two-layered bank (see
Patent Documents 6 and 7).
Further, methods of selective modification of surface properties by
light radiation of a thin organic film formed on the surface are
known (see, e.g., Patent Document 8). Such a thin organic film is
sometimes referred to as a "self-assembled thin organic film." For
example, self-assembled thin organic films are known that undergo
molecular structure changes on exposure to UV light to alter the
water contact angle at the exposed surface.
Techniques have been known that form self-assembled thin organic
films on bank surrounding coating region in which functional layer
is to be formed by a coating method (see Patent Documents 9 and
10). Patent Document 9 reports a method of photo-patterning of a
lyophobic, self-assembled thin organic film provided over entire
surface of partitioning wall (bank) in such a way that the
self-assembled thin organic film exclusively remains on the bank
top surfaces. Patent Document 1: Japanese Patent Application
Laid-Open No. 2004-171007 Patent Document 2: Japanese Patent
Application Laid-Open No. 2005-326799 Patent Document 3: U.S.
Patent Application Publication No. 2005/0116632 Patent Document 4:
Japanese Patent Application Laid-Open No. 2006-216297 Patent
Document 5: U.S. Patent Application Publication No. 2006/017038
Patent Document 6: Japanese Patent Application Laid-Open No.
2007-95512 Patent Document 7: U.S. Patent Application Publication
No. 2007/0071885 Patent Document 8: Japanese Patent Application
Laid-Open No. 2006-188487 Patent Document 9: Japanese Patent
Application Laid-Open No. 2002-237383 Patent Document 10: U.S.
Patent Application Publication No. 2002/0016031
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
As described above, it is expected that a uniform thick coating
film can be obtained by making a lower portion of the bank side
wall lyophilic and making a upper portion of the bank side wall
lyophobic. Thus, the present invention provides a means that allows
precise and full control of the boundary between the lyophilic and
lyophobic areas and thereby provides a means of forming uniform
thick coating films in regions defined by bank.
In the case of a two-layered bank composed of a lower layer made of
inorganic material and a upper layer made of organic material, the
size of a lyophilic area has been adjusted by adjusting the
thickness of the lower layer. Formation of an excessively thick
inorganic lower layer, however, takes longer deposition time;
moreover, over-etching is more likely to occur when etching such an
excessively thick film. Furthermore, over-etching may damage other
members provided underneath the inorganic lower layer.
In view of the foregoing circumstances, the present invention thus
enables easy and precise formation of bank whose inner side surface
is partially made lyophilic (at a lower portion of the inner side
surface). Moreover, coating film thickness is further uniformed by
tapering the bank which define a coating region. The present
invention thus provides an organic EL display panel with less
brightness unevenness by uniformly forming functional layers such
as an organic emitting layer in a region defined by bank in
respective organic EL devices. The present invention also provides
an organic TFT with a highly uniform organic semiconductor
layer.
Means for Solving the Problem
A first aspect of the present invention relates to organic EL
display panels described below.
[1] An organic EL display panel including a plurality of organic EL
devices each including:
a substrate;
an anode formed over the substrate;
an organic emitting layer formed over the anode;
a cathode formed over the organic emitting layer;
a forward tapered bank defining a region for the organic emitting
layer, the bank having a top surface and an inclined side surface;
and
a lyophobic organic film formed on the top surface of the bank and
the upper portion of an inclined side surface of the bank,
wherein a lower portion of the inclined side surface of the bank
includes no lyophobic organic film.
[2] The organic EL display panel according to [1], wherein the
forward tapered bank has a taper angle of 20.degree. to
70.degree..
[3] The organic EL display panel according to [1], wherein the
organic emitting layer is formed by a coating method, and
a contact point between a surface of the organic emitting layer and
the inclined side surface of the bank is defined by the lyophobic
organic film.
[4] The organic EL display panel according to [1], wherein the
lyophobic organic film formed on the bank surface is a
self-assembled film.
[5] The organic EL display panel according to [1], wherein the
lyophobic organic film formed on the bank surface is a monolayer
film.
[6] The organic EL display panel according to [1], further
including a lyophilic organic film formed on the lower portion of
the inclined side surface of the bank.
[7] The organic EL display panel according to [1], wherein the bank
is made of inorganic insulating material.
[8] The organic EL display panel according to [1], wherein the bank
is made of organic insulating material.
[9] The organic EL display panel according to [1], wherein the bank
is a linear bank.
A second aspect of the present invention relates to manufacturing
methods of an organic EL display panel described below.
[10] A method of manufacturing an organic EL display panel
including:
providing a substrate having a plurality of anodes formed
thereon;
forming a forward tapered bank having a top surface and an inclined
side surface so as to surround at least a part of the anode;
forming a lyophobic organic film over a surface of the bank;
exposing the lyophobic organic film at a lower portion of the
inclined side surface of the bank so as to reduce the lyophobicity
of the exposed portion of the lyophobic organic film or remove the
exposed portion of the lyophobic organic film;
applying an ink containing organic luminescent material in a region
defined by the bank to form therein an organic emitting layer;
and
forming a cathode over the organic emitting layer.
[11] The method according to [10], wherein the forward tapered bank
has a taper angle of 20.degree. to 70.degree..
[12] The method according to [10], wherein the lyophobic organic
film is a lyophobic, photosensitive self-assembled film.
[13] The method according to [10], wherein irradiation light used
for the exposure is UV light.
[14] The method according to [10], further including forming a hole
injection layer over the anode prior to the bank formation
step.
A third aspect of the present invention relates to an organic thin
film transistor described below.
An organic thin film transistor including:
a substrate;
a source electrode and a drain electrode which are formed on the
substrate;
an organic semiconductor film for connecting the source electrode
and the drain electrode together;
a forward tapered bank defining a region for the organic
semiconductor film, the bank having a top surface and an inclined
side surface; and
a gate electrode connected to the organic semiconductor film via an
insulating film,
wherein a lyophobic organic film is formed on the top surface of
the bank and a upper portion of the inclined side surface of the
bank, and a lower portion of the inclined side surface of the bank
includes no lyophobic organic film.
Advantageous Effect of the Invention
With the present invention it is made easy to prepare bank whose
inner side surface is partially made lyophilic or lyophobic as well
as to freely control the positions of the lyophilic area and
lyophobic area. It is thus possible to form a highly uniform
functional layer by a coating method in a region defined by a bank
without being influenced by properties (e.g., viscosity) of the
liquid substance to be applied therein. In particular, when the
bank is forwardly tapered, i.e., the bank inner side surfaces are
inclined, the functional layer with much higher uniformity can be
formed by a coating method.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1A and 1B are schematic views showing a lamination of
elements of an organic EL device; FIG. 1A shows an example where a
hole injection layer is not defined by the bank, and FIG. 1B shows
an example where a hole injection layer is defined by the bank;
FIG. 2 is a schematic view showing a lamination of elements of an
organic TFT;
FIGS. 3A and 3B are schematic views demonstrating that when
exposing the bank surface through a mask, the exposure area can be
controlled by changing the distance between the mask and bank
surface;
FIGS. 4A to 4F are a process diagram showing how a liquid substance
supplied to a region defined by the bank dries; and
FIG. 5 shows a model for setting pinning height.
BEST MODE FOR CARRYING OUT THE INVENTION
1. Organic EL Display Panel
An organic EL display panel of the present invention includes a
plurality of organic EL devices, which are typically arranged in a
matrix arrangement. Each organic EL device includes 1) a substrate,
2) a pixel electrode (anode), 3) a functional layer such as an
organic emitting layer, 4) a cathode, 5) a forward tapered bank,
and 6) a lyophobic organic film provided on the tapered bank so as
to cover its top surface and upper portion of inner side surface
(also referred to as "upper portion of the inclined side
surface").
Materials of the substrate are not specifically limited, but are
preferably insulating. Examples include glass, polyethylene
terephthalate (PET), polyethylene naphthalate (PEN), and polyimide
(PI). When manufacturing a bottom-emission type organic EL display
panel, the substrate also needs to be highly transparent to visible
light.
The substrate has a plurality of pixel electrodes on its surface,
which are typically arranged in a matrix arrangement. The pixel
electrodes preferably serve as anodes. Preferably, the pixel
electrodes are each connected to the source electrode or drain
electrode of respective driving TFTs, for example.
When manufacturing a top-emission type organic EL display panel,
the pixel electrodes require light reflectivity. Examples of
materials of light-reflective pixel electrodes include
silver-palladium-copper (APC) alloys, silver-rubidium-gold (ARA)
alloys, molybdenum-chrome (MoCr) alloys, and nickel-chrome (NiCr)
alloys.
On the other hand, when manufacturing a bottom-emission type
organic EL display panel, the substrate and pixel electrode both
require light transparency. Thus, the organic EL display panel is
preferably manufactured by preparing a substrate made of glass,
PET, PEN or the like and providing thereon anodes made of ITO,
indium zinc oxide (IZO), tin oxide or the like.
The organic EL device includes a functional layer which covers at
least a part of the pixel electrode on the substrate. Functional
materials used for the functional layer may be either low-molecular
materials or polymer materials, but are preferably polymer
materials. Polymer material-containing ink can be applied to the
region defined by the bank (later described) relatively easily and
thus is suitable for use in an organic EL display panel of the
present invention. In particular, the organic emitting layer is
preferably made of polymeric organic material. As will be described
later, preferably, ink containing functional material is applied to
the region defined by the bank by inkjet printing, dispensing,
nozzle coating, spin coating, intaglio printing, relief printing,
etc., and dried to form layer therein.
The functional layer prepared by a coating method encompasses at
least an organic emitting layer, and may also encompass a hole
injection layer, an interlayer, an electron transport layer, etc.
These layers are stacked over the pixel electrode.
Examples of organic luminescent materials for the organic emitting
layer include polyphenylenevinylene and derivatives thereof,
polyacetylene and derivatives thereof, polyphenylene and
derivatives thereof, poly(para-phenylene ethylene) and derivatives
thereof, poly3-hexylthiophene and derivatives thereof, and
polyfluorene and derivatives thereof.
The hole injection layer has the function of enhancing the
injection efficiency of holes from the pixel electrode. Examples of
organic materials of the hole injection layer include
poly(ethylenedioxythiophene) doped with poly(styrene sulfonate)
(PEDOT-PSS), poly(3,4-ethylenedioxythiophene) and derivatives
thereof.
The interlayer has the function of preventing electrons from being
transported to the hole injection layer from the organic emitting
layer as well as efficiently transporting holes to the organic
functional layer. Examples of materials of the interlayer include
triphenylamine and polyaniline.
The electron injection layer transports electrons, which have been
injected from the cathode, to the organic emitting layer. Examples
of materials of the electron injection layer include barium,
phthalocyanine, lithium fluoride, and combinations thereof.
A cathode is formed over the functional layer, preferably over the
electron transport layer. Materials of the cathode for a
bottom-emission type organic EL display panel are not particularly
limited as long as they are light reflective; for example, the
cathode is formed of an aluminum layer. In the case of a
top-emission type organic EL display panel, materials that easily
transmit visible light may suffice; for example, an ITO film or the
like may be employed.
The organic EL device may further include a sealing film provided
on the cathode. The sealing film prevents the functional layer of
the organic EL device from being exposed to moisture and air.
Each of the organic EL devices in a organic EL display panel of the
present invention includes bank defining a region in which the
electrode or functional layer is provided. Preferably, the bank
provided on the hole injection layer defines the region for the
functional layer (except hole injection layer) (see FIG. 1A).
Alternatively, the bank provided on the pixel electrode defines the
region for the functional layer (see FIG. 1B).
The bank may be either pixel bank or linear bank, but is preferably
linear bank. The term "pixel bank" refers to a bank which defines a
functional layer region for each organic EL device. The term
"linear bank" refers to a bank defining a functional layer of the
organic EL devices aligned in a row; therefore, in the case of
linear bank, the organic EL devices aligned in a row share one
functional layer.
In the case of pixel bank, coating is conducted by dropping ink
droplets for each region defined by the bank. In the case of linear
bank, on the other hand, coating is facilitated because ink
droplets can be continuously applied in the region defined by the
linear bank. With this linear coating method, not only productivity
increases, but also uniformity in the thickness of the resultant
functional layers improves. Functional layers prepared by coating
methods generally tend to have increased thickness near the bank.
Accordingly, with the pixel bank configuration where the functional
layer is entirely surrounded by bank, the functional layer exhibits
non-uniform thickness at their periphery. With the linear bank
configuration, by contrast, uniform functional layer thickness can
be readily obtained because the functional layer region is free of
any bank in the direction in which pixels are aligned in a row.
It is only necessary for the bank to be made of insulating
material. The bank preferably has resistance to organic solvent as
well as is capable of transmitting some visible light. Moreover,
because the bank may be subjected to etching treatment, baking
treatment or the like, it is preferably made of such material that
exhibits high resistance to those treatments. Materials for the
bank may be organic materials such as resin or inorganic materials
such as glass. Examples of organic materials include acrylic
resins, polyimide resins, and novolac phenol resins. Examples of
inorganic materials include silicon oxide (SiO.sub.2) and silicon
nitride) (Si.sub.3N.sub.4).
The bank is preferably forward tapered and has a top surface and an
inclined side surface. The inclination angle of the inclined side
surface (bank taper angle) is not specifically limited, but is
preferably 20.degree. to less than 90.degree., more preferably
20.degree. to 70.degree., most preferably 30.degree. to 50.degree..
When the bank taper angle is too large, it results in poor sealing
ability due to low coverage of films (e.g., sealing film) over the
bank, facilitating undesired entry of moisture or the like in the
device. When the bank taper angle is too small, it may result in
failure to obtain desired functional layers due to limited ink
amount to be applied for the functional layer formation.
As described above, a lyophobic organic film formed over the entire
surface (including top surface and inclined side surfaces) of the
bank is exposed to light at lower portion of the inclined side
surface so as to remove or modify the exposed portion of the
lyophobic organic film. In order to selectively and precisely
expose the lyophobic organic film at lower portion of the inclined
side surface of the bank, the bank is preferably forward tapered,
with the taper angle preferably ranging from 20.degree. to
70.degree..
The bank height is not specifically limited, but is about 0.3 to 3
.mu.m.
The bank is preferably lyophobic at its top surfaces because the
ink applied to the region defined by bank may leak beyond the bank
top surface. The bank is characterized in that its inclined side
surface is partially lyophobic and lyophilic. More specifically,
the inclined side surface is lyophilic at a lower portion and is
lyophobic at an upper portion.
Herein, the terms "lyophobic" and "lyophilic" are used in a
relative sense; it is only necessary that the inclined side surface
be more lyophobic at a upper portion than at a lower portion.
Preferably, the term "lyophobic" means that a droplet of
water-based ink to be applied for the functional layer formation
has a contact angle of 80.degree. or more, and a droplet of organic
solvent-based ink to be applied for the functional layer formation
has a contact angle of 40.degree. or more. The term "lyophilic"
preferably means that a droplet of organic solvent-based ink has a
contact angle of 5.degree. or less.
As described above, the bank top surface and upper portion of the
bank inclined side surface are made lyophobic. To establish
lyophobicity, it is preferable to provide a lyophobic film,
particularly a lyophobic organic film, on the top surface and upper
portion of the inclined side surface. Moreover, the lyophobic film
preferably is a photosensitivity film that changes from lyophobic
to lyophilic on exposure to light. Utilizing this photosensitivity,
lower portion of the bank inclined side surface can be made
lyophilic.
The lyophobic film is preferably a monolayer film, more preferably
a self-assembled monolayer film. The reason for this is that
monolayer film has less influence on the functional layer to be
formed in the region defined by the bank. A self-assembled layer is
a monolayer of chain molecules in which one end of the molecules
has a functional group showing a specific affinity to the
substrate. More specifically, the self-assembled layer is prepared
by the chemisorption of the functional groups onto a substrate from
either the vapor or liquid phase, so that the functional groups
form bonds with the atoms of the substrate surface. This monolayer
film is referred to as a self-assembled film as it is formed by the
self-chemisorption of molecules onto a substrate.
A self-assembled film that changes from lyophobic to lyophilic on
exposure to light may be prepared using the technique disclosed by
Patent Document 8. More specifically, a self-assembled film is
prepared by coating a substrate with a solution of phenylsulfone
bearing a functional group which can interact with the substrate
(silyl group) and by drying the solution. The obtained film is
lyophobic, but is made lyophilic on exposure to UV light by the
molecular structure change.
Similarly, a self-assembled film that changes from lyophobic to
lyophilic on exposure to light may be prepared using the technique
disclosed by Japanese Patent Application Laid-Open No. 2007-246418.
More specifically, a self-assembled film is prepared by coating a
substrate with a solution of a compound bearing a functional group
which can interact with the substrate (silyl group) and a secondary
amine capped with o-nitrobenzyloxycarbonyl group and by drying the
solution. The obtained film is lyophobic, but is made lyophilic on
exposure to UV light by the molecular structure change. An organic
coating film may also be prepared which is disclosed by Japanese
Patent Application Laid-Open No. 2006-168606.
Alternatively, a lyophobic organic thin film (e.g., a
self-assembled film made of fluoroalkylsilane) may be formed using
the technique disclosed by Japanese Patent Application Laid-Open
No. 2007-134348. This lyophobic organic thin film is ablated by
irradiation with light, thereby exposing the substrate.
Any one of these lyophobic self-assembled films is formed, which is
then partially exposed to light at selected portion, so that the
exposed portion is made lyophilic.
FIGS. 1A and 1B each show an example of an organic EL device in an
organic EL display panel of the present invention. The organic EL
devices of FIGS. 1A and 1B are each placed over a driving TFT
because they are intended for use in a top-emission type organic EL
display panel. It is, of course, possible to apply the present
invention to a bottom-emission type organic EL display panel; in
this case, driving TFTs may be formed on the same plane as organic
EL devices.
FIG. 1A shows an organic EL device arranged on planarizing film 3
covering substrate 1 in which TFT 2 is provided. More specifically,
reflective anode 4 (pixel electrode) is arranged on planarizing
film 3, and hole injection layer 5 is arranged on reflective anode
4. Reflective anode 4 (pixel electrode) is connected to the drain
electrode (not shown) of TFT 2.
Forward tapered bank 9 is formed surrounding hole injection layer
5. Bank 9 partially overlaps hole injection layer 5. In the region
defined by bank 9, interlayer 6, emitting layer 7, and electron
injection layer 8 are sequentially laminated. Among these layers,
it is preferable that at least emitting layer 7 be prepared by a
coating method. Cathode 10 and sealing film 11 are further
laminated. Cathode 10 and sealing film 11 may be connected to
adjacent organic EL devices beyond bank 9. Similarly, electron
transport layer 8 may be connected to adjacent organic EL devices
beyond bank 9.
FIG. 1B also shows an organic EL device arranged on planarizing
film 3 covering substrate 1 in which TFT 2 is provided. Bank 9 is
formed surrounding reflective anode 4 (pixel electrode) arranged on
planarizing film 3. Bank 9 partially overlaps reflective anode 4.
In the region defined by bank 9, hole injection layer 5, interlayer
6, emitting layer 7, and electron injection layer 8 are
sequentially laminated. Among these layers, it is preferable that
at least emitting layer 7 be prepared by a coating method. Cathode
10 and sealing film 11 are further laminated.
Bank 9 may be either pixel bank or linear bank. A pixel bank
completely surrounds respective pixel electrode to define separate
pixel. On the other hand, a linear bank defines rows of pixels; it
partially surrounds pixel electrodes. More specifically, linear
bank defines a row of pixels of the same color (R, G or B)
In FIGS. 1A and 1B, lyophobic film 12 is formed on bank 9 so as to
cover its top surface and a upper portion of its inclined side
surface. On the other hand, lyophilic film 12' is preferably formed
on a lower portion of the inclined side surface. Lyophobic film 12
or lyophilic film 12' may be decomposed and remain as residues
after the device has been manufactured. These residues are also
defined as lyophobic film 12 or lyophilic film 12'.
The position at which a droplet of ink (ink for an emitting layer
is employed herein) applied in a region defined by the bank shows
"self-pinning" when it has reached the critical concentration
during drying is herein referred to as "pinning point" 13. As will
be described later, the position of the pinning point can be
controlled by adjustment of the boundary between the lyophobic film
area and lyophilic film area. It is thus possible to provide
uniform thick emitting layer 7. Accordingly, the pinning point
corresponds to a contact point between a surface of the coated
layer (including emitting layer 7) and an inclined side surface of
the bank.
Pinning point 13 generally positions above the uniform-thick area
of emitting layer 7 (upper portion of the bank). Pinning point 13
often positions at the same level as the surface of the cathode or
sealing film laminated on the electron injection layer which is
often a ultrathin film of several nanometers in thickness (see FIG.
1B). More specifically, a contact point between a surface of a
coated layer (including emitting layer 7) and a bank inclined side
surface is often at the same level as the height of the surface of
the cathode or sealing film.
There is no need to provide a lyophobic film on a lower portion of
the inclined side surface below pinning point 13; rather, it is
preferable that no lyophobic film is provided thereon. When the
inclined side surface is made entirely lyophobic, it repels ink
containing functional layer material at the bank bottom, which may
result in failure to cover the edge of the pixel electrode with a
functional layer. This may cause a short circuit between the
cathode and anode.
The present invention also provide an organic thin film transistor
(organic TFT) described below (see FIG. 2). The organic TFT shown
in FIG. 2 includes substrate 20; gate electrode arranged on
substrate; gate insulating film 22 covering gate electrode 21;
source electrode 23 and drain electrode 24 arranged on gate
insulating film 22 and a channel region; forward tapered bank
respectively covering source electrode 23 and drain electrode 24;
organic semiconductor layer 25 arranged in a region defined by bank
26; and overcoat layer 28 covering bank 26 and organic
semiconductor layer 25.
Lyophobic film 29 (including decomposed matter in the form of
residues) is formed on the top surface and a upper portion of the
inclined side surface of bank 26. On the other hand, lyophilic film
12' (including decomposed matter as residues) is preferably formed
on a lower portion of the inclined side surface. By adjusting the
position of pinning point 30 by adjusting the position of the
boundary between the lyophobic film area and lyophilic film area,
it is possible to control the thickness and uniformity of the
organic semiconductor layer prepared by a coating method.
2. Manufacturing Method of Organic EL Display Panel
A manufacturing method of the organic EL display panel of the
present invention includes, for example, the steps of:
1) providing a substrate having a plurality of anodes formed
thereon;
2) forming a tapered bank so as to surround at least a part of the
anode;
3) forming a lyophobic organic film over a surface of the bank;
4) exposing the lyophobic organic film at a lower portion of an
inclined side surface of the bank so as to reduce the lyophobicity
of the exposed portion of the lyophobic organic film or remove the
exposed portion of the lyophobic organic film;
5) applying ink containing organic luminescent material in a region
defined by the bank to form therein an organic emitting layer;
and
6) forming a cathode over the organic emitting layer.
Formation of anodes (pixel electrodes) on a substrate can be
achieved by vapor deposition, or sputtering, of anode material.
Photolithography can also be employed. Anodes are preferably
arranged on the substrate in a matrix arrangement or in a linear
arrangement.
Hole injection layers may be formed on the anodes arranged on the
substrate. The formation method of hole injection layer is not
specifically limited.
Tapered bank may be formed by photolithography, for example, as
follows: A resin film is applied over the substrate surface
provided with anodes and optionally with hole injection layers; the
resin film is selectively exposed through a mask; and desired
portions of the resin film are developed away. In this way the
anodes or hole injection layers arranged on the substrate become
exposed at the surface. Alternatively, tapered bank made of
inorganic material may be formed by CVD or the like. As described
above, the bank may be either pixel bank or linear bank, but is
preferably linear bank.
Subsequently, a lyophobic organic film is formed over surfaces of
the bank. The lyophobic organic film may be formed not only on the
bank surface, but also in the region defined by the bank (anode
surface and/or hole injection layer surface). The lyophobic organic
film is preferably a photosensitive film that changes from
lyophobic to lyophilic on exposure to light due to lyophobicity
reduction. Moreover, the lyophobic organic film formed on the bank
surface is preferably an organic monolayer film or self-assembled
film. The reason for this is that organic monolayer film has less
influence on functional layer to be formed in the region defined by
the bank.
The method of forming a lyophobic organic film, particularly a
self-assemble film, on the bank surface is not specifically
limited; for example, a solution containing organic molecules for a
lyophobic organic film is applied on the bank surface using a known
coating technique, and is dried by heating to prepare a lyophobic
organic film. Examples of coating methods include dip coating, spin
coating, spray coating, roll coating, Meyer bar coating, screen
printing, and brush coating. More specifically, the above-described
prior art can be employed.
The lyophobic organic film formed on the bank surface preferably
has a property that alters its physical properties on exposure to
light. For example, on exposure to UV light, exposed portion of the
lyophobic organic film exclusively becomes lyophilic.
Alternatively, exposed portion themselves may be ablated. When the
exposed portion of the lyophobic organic film is removed, member
which have been covered by the lyophobic organic film become
exposed at the surface, whereby lyophobicity disappears and thus
lyophilicity relatively increases at the exposure site.
Thus, the lyophobic organic film formed on the bank surface is
partially exposed to light, to make the lyophobic organic film of
the exposed portion be lyophilic. Here, lower portion of the
inclined side surface of the bank is exposed to light and thereby
made lyophilic. When a lyophobic organic film is also formed in the
region defined by the bank, it is preferable that the lyophobic
film in this region be also exposed to light.
Selective exposure of the lyophobic film formed on the bank surface
may be achieved by exposure using a mask. The exposure area may be
controlled by adjusting the opening area of the mask or the
distance (gap) between the mask and bank surface. Because light 32
passing through the mask opening spreads out as shown in FIGS. 3A
and 3B, the exposure area can be made large by widening the
distance between mask 31 and bank surface. In FIG. 3A, the distance
between mask 31 and bank surface is small compared to that of FIG.
3B. Thus, in FIG. 3B, light 32 spreads out more and, therefore, the
exposure area shown in FIG. 3B is larger than that shown in FIG. 3A
even though the mask opening is of the same size as that of FIG.
3A.
As described above, lower portion of the inclined side surface of
bank is made lyophilic. Preferably, an area to be made lyophilic
(area to be exposed to light) is so selected that resulting
functional layers, particularly an organic emitting layer, exhibits
high uniformity in thickness, because organic emitting layers with
high uniformity in thickness effectively contribute to improved
image quality, e.g., low brightness unevenness.
The area to be made lyophilic may be appropriately selected
depending on 1) bank taper angle; 2) properties (e.g., receding
contract angle) of liquid raw material of the functional layer; 3)
setting of exclusion area; and so forth, so that resultant
functional layers become highly uniform in thickness. A specific
setting scheme for this will be described in detail below.
Once lower portion of the inclined side surface of the bank has
been made lyophilic, functional layer is formed by a coating method
in the region defined by the bank. As described above, the
functional layers are preferably formed by applying ink containing
functional material by a coating method such as inkjet printing,
dispensing, nozzle coating, spin coating, intaglio printing or
relief printing and drying the ink applied therein. Thereafter,
cathodes and sealing films are sequentially formed. In this way
organic EL devices are manufactured.
Setting of Area to be Made Lyophilic
The following describes a non-exclusive method of setting an area
of the bank surface to be lyophilic. Herein, the area of the
inclined side surface from the bottom to a given height
(hereinafter also referred to as "pinning height") is set as an
area to be made lyophilic.
The liquid substance (ink) in the form of droplet 40 supplied to
the cavity defined bank 26 has a contact angle of .theta. with
respect to the bank surface (here, top surface 9-1) (FIG. 4A). As
droplet 40 dries, contact angle .theta. decreases (FIG. 4B) to a
level equal to receding contact angle .theta..sub.R of the ink.
Receding contact angle .theta..sub.R varies depending on ink's
properties (e.g., viscosity) as well as on bank surface's physical
properties (e.g., surface free energy). Namely, the more lyophobic
the bank surface is to ink, the greater receding contact angle
.theta..sub.R becomes.
When contact angle .theta. equals to receding contact angle
.theta..sub.R, droplet 40 becomes small, and the edge of droplet 40
approaches toward bank edge 9-3 (FIG. 4C). When the edge of droplet
40 has reached bank edge 9-3, contact angle .theta. of the ink with
respect to bank surface (inclined side surface) increases to
.theta.' (FIG. 4D). As the ink further dries, contact angle .theta.
decreases (FIG. 4E). When contact angle .theta. equals to receding
contact angle .theta..sub.R, droplet 40 becomes small (FIG. 4F). As
the ink dries, ink concentration increases, which result in
increasing ink viscosity. Thus, the size of droplet 40 does not
change any more, which result in determining the final position of
the droplet edge. The above-described droplet edge positioning
process is referred to as "pinning." "Pinning" that occurs due to
ink concentration increase is particularly referred to as "self
pinning."
The present invention is characterized in that "pinning" is
controlled by making a lower portion of a bank inclined side
surface lyophilic while making a upper portion thereof lyophobic.
Specifically, since ink's receding contact angle .theta..sub.R
becomes small at a lyophilic bank surface, the ink droplet becomes
hard to be small further. Thus, the boundary between the lyophobic
area and lyophilic area corresponds to the droplet edge position,
thereby enabling "pinning" control.
The following discusses examples where ink's receding contract
angles .theta..sub.R are 30.degree. and 40.degree., respectively,
with respect to a lyophilic surface (lower portion of an inner side
surface) of a bank.
Here, a case in which a hole injection layer (HIL), an interlayer
(IL), an organic emitting layer (EML)) are sequentially stacked
over an anode arranged in a region defined by bank will be taken as
example. As shown in FIG. 5, the thicknesses of these layers at
effective pixel edge 45 are set as follows: HIL: 65 nm, IL: 20 nm,
EML: 85 nm (total height h: 170 nm). As shown in FIG. 5, there is a
non-effective pixel area called "exclusion area" between bank 9 and
effective pixel edge 45. In this example, the width of the
exclusion area from the bank edge is defined as distance c (: 1
.mu.m or 0.5 .mu.m). The bank taper angle .alpha. is set to
30.degree. to 90.degree..
When the height of the lyophilic area in bank tapered surface 9-2
is defined as pinning height H (unit: nm), the following equation
holds:
.times..times..alpha..times..function..alpha..theta.
##EQU00001##
Values of pinning height H obtained using the above equation are
shown in the table below.
TABLE-US-00001 TABLE 1 Ink receding Ink receding contact angle
contact angle (.theta..sub.R = 30.degree.) (.theta..sub.R =
40.degree.) Exclusion Exclusion Exclusion Exclusion area area area
area (c = 1 .mu.m) (c = 0.5 .mu.m) (c = 1 .mu.m) (c = 0.5 .mu.m)
Taper 30.sup.note(1) 193 184 -- -- angle 35 293 242 -- --
(.alpha..degree.) 40.sup.note(2) 438 322 191 182 45 598 416 281 233
50 757 500 400 300 55 940 597 543 376 60 1120 685 662 438 65 1298
776 807 512 70 1463 855 936 576 75 1602 918 1060 634 80 1722 968
1188 694 85 1806 1000 1281 733 90.sup.note(3) 1886 1030 1347 760
.sup.notes(1)to(3)For convenience of calculation, values of taper
angle were set at 31, 41 and 89, respectively.
As described above, pinning height (height of the bank inner side
surface to be made lyophilic) is appropriately determined depending
on the relationship between ink property and bank surface (ink's
receding contact angle) and setting of the exclusion area. This
makes it possible to pin the functional layers at any desired
position and thus to obtain high uniformity in the thickness of the
functional layers.
EXAMPLES
A matrix of multiple anodes, each 190 .mu.m.times.60 .mu.m in size
and 50 .mu.m in thickness, was arranged on a glass substrate by
sputtering. APC (Ag--Pd--Cu) alloy was employed as the anode
material.
Linear bank (material: silicon oxide) was formed by CVD which
surrounds the anodes formed on the substrate. The bank height was
set at 1 .mu.m, and bank taper angle was set at 45.degree.. A
lyophobic self-assembled film was formed over the bank surface and
the region defined by the bank (anode surfaces). Portion of the
self-assembled film was exposed to UV light through a mask at a
dose of 8 J/cm.sup.2. The exposure area was bank inclined side
surface from the bottom to 600 nm height.
In the region defined by linear bank, a PEDOT-containing solution
was applied and dried to form PEDOT layer (thickness: 65 nm) as
hole injection layer. A 0.8 wt % triphenylamine solution in anisole
was applied over the hole injection layer and dried to form thereon
interlayer (thickness: 20 nm). A 1.3 wt % polyfluorene solution in
cyclohexylbenzene was applied over the interlayers and dried to
form thereon emitting layer (thickness: 85 nm). Further, electron
injection layer (thickness: 5 nm) was formed over the emitting
layer by vacuum deposition of barium.
A cathode (material: ITO, thickness: 100 nm) was formed over the
electron injection layer by facing target sputtering. Finally, a
sealing film was formed.
The present application claims the priority of Japanese Patent
Application No. 2008-064818 filed on Mar. 13, 2008, the entire
contents of which are herein incorporated by reference.
INDUSTRIAL APPLICABILITY
The present invention can improve uniformity of functional layers
including organic emitting layers prepared using so-called coating
methods, contributing to provide a high-quality organic EL display
panel with less brightness unevenness.
EXPLANATION OF REFERENCE NUMERALS
1: Substrate 2: TFT 3: Planarizing film 4: Reflective anode 5: Hole
injection layer 6: Interlayer 7: Emitting layer 8: Electron
injection layer 9: Bank 9-1: Bank top surface 9-2: Bank inner side
surface 9-3: Bank edge 10: Cathode 11: Sealing film 12: Lyophobic
film 12': Lyophilic film 13: Pinning point 20: Substrate 21: Gate
electrode 22: Gate insulating film 23: Source electrode 24: Drain
electrode 25: Organic semiconductor layer 26: Bank 28: Overcoat
layer 29: Lyophobic film 29': Lyophilic film 30: Pinning point 31:
Mask 32: Irradiation light 40: Droplet 45: Effective pixel edge
* * * * *